1. Field of the Invention
The present invention concerns a circuit, a system, and a method for communication between two nodes of a radio network.
2. Description of the Background Art
In a radio network, it is desirable to find the position of the nodes of the radio network or at least to determine a distance between the nodes. By this means, a faulty node can be found easily, for example. In addition, slow movements of a node, such as of a means of transport in a factory, can be tracked. Position finding can also be used in firefighting when the nodes dropped from an airplane report a location-specific elevated temperature.
Known from U.S. Pat. No. 5,220,332 is a range finding system with an interrogator and a transponder that permits non-simultaneous measurements between two objects. A carrier signal is modulated with a (low-frequency) modulation signal with a variable modulation frequency in order to determine a distance between the interrogator and the transponder from the change in the modulation signal by means of a phase measurement or alternatively a transit time measurement.
From WO 02/01247 A2 is known a method for measuring distance between two objects using electromagnetic waves. An interrogation signal from a base station and a response signal from a portable code transmitter are transmitted twice at different carrier frequencies. In this system, the carrier frequencies are correlated, which is to say that they are dependent on one another. The carrier frequencies are matched to one another so that a phase shift between the signals can be measured. The distance of the code emitter from the base station is calculated from this phase shift. The interrogation signal and the response signal can be transmitted at different carrier frequencies or at the same carrier frequency.
If a transceiver of a node for a sensor network is designed in conformance with the industry standard IEEE 802.15.4, then the transceiver cannot simultaneously transmit and receive.
From U.S. Pat. No. 6,731,908 B2 is known a method for determining the distance between two objects for the Bluetooth technology. In this method, the frequency is changed by frequency hopping in order to measure a phase offset for multiple different frequencies. An object has a voltage controlled crystal oscillator in a phase locked loop (PLL), wherein the phase locked loop is closed during reception and opened during transmission so that the receive signal and transmit signal have the same frequency. The phase of the local oscillator signal of the voltage controlled crystal oscillator is coherent with the received signal due to the synchronization by means of the PLL.